A SiOx powder is used as a deposition material to form a deposited film of SiOx on a food packaging film or an optical component because of its high vapor pressure. For example, it is used as a material to form a gas barrier film comprising a SiOx film on a food packaging film to prevent permeation of water vapor or oxygen gas to prevent deterioration of food.
Conventionally, as a method for producing a SiOx powder, a method wherein a mixed material containing silica and metal silicon and/or carbon is subjected to a high temperature treatment in a non-nitriding atmosphere under at least 8×104 Pa to form a SiO-containing gas, which is cooled at a cooling rate of at most 1000° C./sec (JP-A-2001-158613), a method wherein a SiO2 powder is heated in incomplete combustion flame to form Si vapor, which is suboxidized (JP-A-5-213606), etc., have been known.
In order to make the SiOx powder have a high purity in such conventional methods, it is necessary that impurities are not mixed during the time from preparation of a material to collection of a product. However, a special treatment such as purification is required to make the material have a high purity. Further, in order to generate SiO vapor or Si vapor by heating the material, a high temperature operation at from about 1500 to about 2000° C. is required. In such a case, even if a high purity material is employed, impurities such as Na, Al, Mg, Ca and Fe are mixed from e.g. the furnace material, and it is difficult to produce a high purity SiOx powder.